Create Extension Method for Barcode and QRCode commands

[igorocampos]

Dependent on #29

Once the new Barcode and QRCode methods are created, we can create methods that will extend a string (the barcode data) like this

public static byte[] ToBarcode(this string barcode, BarCodeType barCodeType, int heightInDots = 162, BarcodeWidth barcodeWidth = BarcodeWidth.Normal )
  => Commands.Barcode(barCodeType, barcode, heightInDots, barcodeWidth);